Magnetic data transducer heads produce an electrical output signal having a level which is proportional to the amount of magnetic flux transduced from a disk data storage surface, and therefore make excellent position transducers for a head position servo loop of a disk drive.
In one arrangement, servo positioning signals are recorded in a phase coherent, side-by-side relationship, so that as the head passes over half of each track, the patterns result in electrical signals which are integrated in the head. If the head is exactly between the two side-by-side patterns, a resultant position error signal put out by the head is zero. Sometimes, a dibit pulse pattern is employed, and one example of a peak detector for sampling and holding pulse peaks from a dibit servo pattern is described in U.S. Pat. No. 4,477,849. Apparatus enabling detection of a true average of N signal samples is described in U.S. Pat. No. 5,868,470. This latter approach employed two capacitors in an analog arrangement.
In another arrangement, radially offset, circumferentially staggered servo bursts provide servo head positioning information. In this latter arrangement, relative amplitudes of the single-frequency burst fields are sampled and held, converted to digital values and compared to develop a position error signal (PES). An example of a peak detector for sampling and integrating staggered burst fields is provided in commonly assigned U.S. Pat. No. 4,669,004 to Moon et al, particularly in conjunction with the description of FIG. 13 thereof. The disclosure of the '004 patent is incorporated herein by reference.
Ideally, a peak detector will acquire a peak value of a burst very rapidly. Once the value is acquired, the peak detector ideally will appear to an analog to digital converter as manifesting an infinite hold time. In other words, once a peak is acquired, it is held until the peak detector is reset. One approach known in the prior art is to arrange a peak detector as having a master portion, and a slave portion. The master portion desireably manifests a sharp rise characteristic which follows each pulse to its peak. The slave portion essentially follows the master portion, but only while the master portion is actively following a rising edge of an incoming waveform. After the master begins its decay, the slave effectively disconnects from the master, and maintains its output at, or near the peak of the signal being followed. A benefit of this arrangement is that the amplitude of each pulse peak will be caught by the master and saved by the slave. If one has the capability of processing each peak with a fast analog to digital processor, it is possible to average the noise. However, if the noise is not averaged, the master-slave arrangement catches what is effectively the amplitude of the last pulse peak of the burst. So, if the detected burst sequence includes ten pulse peaks, and the peak detector circuit does not effectively process each one, or multiple ones of them, the value available for processing will effectively be the last peak of the burst being held.
One example of a conventional master-slave peak detector of the type being described above is the ATT 91C012 low power REACH1 device. While this device generally worked well, as track densities have increased with narrower tracks, problems have arisen with noise, including chaotic noise. A hitherto unsolved need has arisen for an improved peak detector of the master-slave type enabling weighted averaging, which thereby realizes improved performance in the presence of higher levels of noise attributable to smaller effective track widths.